Yes, you definitely can, but remember you are competing with a million other agencies who do the same.

It will be essential to have a USP.

You could learn PHP or hire someone to offer custom coded WordPress websites with unique themes and plugins of your own.

When you offer websites based on existing themes, remember there is always competition in the crowded space of WordPress design.

In the case of e-commerce websites, although woocommerce is good, it’s not so efficient when it comes to a huge library of products.

Offer Magento based websites for large scale e-commerce businesses.

Another strategy could be to niche down your agency to a specific industry.

For example, a WordPress agency specialized in Plumbing, HVAC and related businesses.

In this way, apart from websites, you get a chance to upsell the clients offering complete marketing solutions like SEO, Social media marketing, etc.

Also, you can earn authority in that specific niche and get a lot more referrals.

Hope it helped.